Hydraulic power transmission systems



June 8, 1965 Y D. FIRTH ETAL 3,187,493

HYDRAULIC POWER TRANSMISSION SYSTEMS Filed March 1, 1963 VAR/ABLE VALVE /X ENG/NE BY P455 56. 4 5 5 VALVE [I 2.

'Lfil J THERMOSTAT/C M 0/4 55mm CONTROL 5 VALVE OIL SIDE OF EXCHANGER 5 /5 5&2.

3,187,498 HYDRAULIC POWER TRANSMISSION SYSTEMS Donald Firth and Roger Harvey Yorke Hancock, East Kilhride, Glasgow, Scotland, assignors to Councilfor Scientific and Industrial Research, London, England, a body corporate of England Filed Mar. 1, 1963, Ser. No. 262,124 Claims priority, application Great Britain, Mar. 9, 1962,

Claims. ici. Cl. 60-49) United States Patent rise unduly, and cooling of the oil becomes necessary. At 7 the same time, when starting from a cold condition, the viscosity of the oil may be too high for efficient operation, and the oil requires heating. There is thus a relatively clearly defined optimum temperature range for the oil which results in optimum efiiciency.

The present invention provides a system for the control of the oil temperature by causing it to traverse a heat exchanger in which the other heat exchange fluid is the cooling water for the prime mover. By suitably controlling the rate of feed of cooling water to this heat exchanger and, if desired, by varying the point in the cooling water circuit from which it is derived, a close control can be exercised on the oil temperature under normal working conditions.

Preferably, the control of the rate of feed of the cooling water to the oil/water heat exchanger, and the optional selection of the point of derivation of the coolingwater input thereto, are carried out automatically in response to changes in the temperatures of the oil and the water at given points in their respective circuits.

Advantageously, the cooling water circuit includes an auxiliary radiator.

In this specification, the term cooling water has its ordinary connotation and includes solutions of antifreeze, anti-corrosion, or other customary additives, whilst the term oil includes all the normal substances used in hydraulic power transmissions, and special compounds designed to suit particular operating requirements.

A system according to the present invention provides for a transfer of heat in either direction, so that some measure of control is exercised on the temperature of the cooling water. t

One practical embodiment of ,the present invention, as applied to a vehicle transmission powered by a conventional internal combustion engine, will now be particularly described, by way of example, with reference to the accompanying drawingsin which: j

FIGURE 1 is a diagram of the cooling water circuit showing the oil/water heat exchanger; and

FIGURES 2 to 4 indicate those parts of the circuit which are operative 'under specified conditions.

Referring first to FIGURE 1, the hydraulic transmission system includes a pump P and a motor, M of con ventional design. The transmission pump P is driven by a water-cooled internal combustion engine 1 the cooling water for which is circulated by a water pump 2. in conventional manner. The outlet from the water jacket of the engine is coupled to a two-way differential distribution valve 3 of known type which varies the ratio between the 3,187,498 Patented June 8, 1965 lice connected to the main radiator 6 for the prime mover 1 whilst the outlet 5 is directly connected to the inlet to the water element 7 of an oil/water heat exchanger 8. The oil element 9 of this latter is connected in the hydraulic power transmission circuit of which a part is indicated at 10.

The outlet from the main radiator 6 passes directly to a second two-way differential distribution valve 11, the outlet 12 of which feeds water direct to the cooling water pump 2. The other valve outlet 13 leads to an auxiliary radiator 14 which is connected direct to the inlet of the water element 7 of the oil/water heat exchanger.

The position of the valve 3 is governed by a thermostat, indicated at 15, which is responsive to the temperature ,of the water at the outlet from the water jacket of the prime mover 1, whilst the valve 11 is controlled by a thermostat 16 in the outlet from the oil element 9 of the heat exchanger 8. The latter is also shown in the drawing as controlling a bypass valve 18 which can, in an emergency, short-circuit the valve 3 and feed all the cooling water flow to the main radiator 6. Such action may be required if there is an abnormal rise in oil temperature, or if the thermostat 15 fails or is slow to set the differential valve 3 to open the outlet 4. This by-pass may be omitted.

In use, when starting from a cold condition, the thermostat 15 sets the differential valve 3 to open the outlet 5 and the thermostat 16 sets the differential valve 11 to open the outlet 12. The circuit is then as shown in FIG. 2. As the prime mover 1 warms up, the temperature of the cooling water rises and heat is transferred to the oil in the heat exchanger 8, thus accelerating the rate at rates of fiow through two outlets 4, 5. The. outlet 4 is which the oil in the hydraulic transmission circuit 10 reaches its optimum working temperature.

During the warming up period, the valve 3 is moved to progressively close the outlet 5 and open the outlet 4, tending to assume the position shown in FIG. 3 where the full flow of cooling water is being circulated through the main radiator 6, and returned direct to the pump 2.

While this progressive change-over is occurring in the cooling water circuit, less water is being passed through the element 7, and the rate of heat transfer to the oil decreases. The arrangement is such that under normal operating conditions the oil in the element 9 requires relatively little cooling, and the thermostat 16 keeps the 'dilferential valve 11 set to return at least the greater proportion of the cooling water direct from the main radiator 6 to the pump 2.

If, now, the oil temperature in the hydraulic transmission circuit 10 rises above the maximum set by the thermostat 16, the later moves the valve ,11 to divert some water through the outlet 13 to the auxiliary radiator 14 and thence through the water element 7 back to the pump 2. The water entering the heat exchanger is thus cooled below the outlet temperature from the main radia tor 6 and extracts heat from the oil. If due to, say, prolonged retardation, the oil temperature continues to rise, the thermostat 16 ultimately sets the valve 11 to the position shown in FIG. 4, where the full flow of cooling water is circulated through the auxiliary radiator 14 and the heat exchanger 8. This is the condition of maximum heat loss by the cooling water to atmosphere, coupled with maximum heat absoption from the oil.

As the temperature of the oil falls to its optimum value as determined by the setting of the thermostat 16, the

flow of ooolingwater through the auxiliary radiator 14 and the heat exchanger 8 is progressively reduced by the progressive return of the differential valve 11 to the position shown in FIG. 3. Both diiferential valves 3,11 automatically distribute the cooling water flow to the ditterent paths in the proportions called for by the particular operating conditions of the system. a i

In a typical system, the normal operating temperatures would be approximately as follows:

Cooling water circuit (FIG. 4)

Thermostat set to open outlet 4 fully at 160 F.

Oil circuit (FIG. 4) Inlet to oil element 9 180 Outlet from element 9 150 Thermostat 16 set to open outlet 13 fully at 150 F.

A system according to the presentinvention takes advantage of the fact that, for a given size of radiator, and a given difference between liquid and air inlet temperatures in a radiator, more heat can be extracted per unit of time from water than from oil. Hence, the invention leads to more efficient cooling of the oil, whilst the two-way heat transfer in the oil/water heat exchange promotes a more rapid attainment of optimum temperatures in each liquid under different operating conditions. Thus, for example, where the system according to the invention is applied to a vehicle, the oil temperature is raised more rapidly to its optimum valve after a cold start than would otherwise be the case when the transmission is continuously driving. On the other hand, the cooling water is raised more rapidly to its optimum temperature if the transmission is continuously retardingas, for example, during a continuous descent from a cold start.

Other advantages of a system according to the present invention are that by using a common heat exchanger between the two liquid circuits a greater economy of weight andspace occupied by equipment can be achieved; and also that items of equipment such as valves, radiators, and thermostats are normally more readily available for the water circuit than for the oil circuit. 7

Each two-way dilTerential-acting valve 3, 11 can be of conventional design in which the inlet port is permanently connected to the inlet circuit and outlet ports are variable and dilferentially obturated by the valve member. For example, the latter may be of hollow cylindrical from having its bore in permanent communication with the inlet circuit and having an arcuate radial outlet port through its cylindrical wall. The cylindrical valve memher is a fluid-tight rotary fit in a cylindrical bore of the valve body, the latter having a pair of adjacent separate outlet ports each registrable with the outlet port in the valve member and preferably coextensive therewith when in' full registration. The circumferential gap-between the outlet, ports is sufficient to' ensure a satisfactory fluid seal between them when the valve member is moved to either limit of its rotary travel so that, in either limit position, one outlet port in the body is fully open while the other is fully closed. As will be understood, the ports in-the body may be at different levels in the direction of the axis of the cylindrical valve member, and the latter may havecorrespondingly axially displaced outlet ports to register respectively therewith in the differential manner described above. 7 c

In an alternative arrangement, each two-way difierential-acting valve 3, 11 may consist of a pair of conventional oneway valves connected to a common inlet but having their outlets connected to respective outletcircuits,

4 heat exchange system comprising an oil/water heat exchanger having its water element adapted to be connected in the water cooling circuit of the prime mover and its oil element adapted to be connected to the oil circuit of the transmission; a cooling water radiator; a. two-Way differential-acting valve for dividing the total flow of cooling water in varying proportions between said radiator and said heat exchanger water element and having its inlet connected to the outlet of the prime mover water jacket, one outlet connected to said radiator and the other outlet connected to the inlet of said water element; connections from the outlet of said radiator to said water element and to the inlet of said water jacket; and temperature-responsive elements in the outlet of said water jacket and in the outlet of said oil element for controlling the flow of water through said water element.

2. For use in an hydraulic power transmission system adapted to be driven by a water-cooled prime mover, a heat exchange system comprising an oil/Water heat exchanger having its Water element adapted to be connected in thewater-cooling circuit of the prime mover and its oil element adapted to be connected to the oil circuit of the transmission; a cooling water radiator; a first two-way differential-acting valve for dividing the flow of cooling water from the prime mover water jacket between the inlets to said radiator and to said water element; a second two-way differential-acting valve for dividing the flow of cooling water from said radiator to inlets to said Water jacket and to said Water element; a first temperature-sensitive element in the outlet from said Water jacket for controlling the position of said first two- Way valve, and a second temperature-sensitive element in the outlet from said oil element for controlling the position of said second two-Way valve.

3. A heat-exchange system as claimed in claim 2 in cluding an auxiliary radiator interposed in the cooling water circuit between said second two-Way valve and the inlet to said Water element.

4. For use in an hydraulic power transmission system adapted to be driven by a water-cooled prime mover, a heat exchange system comprising an oil/ water heat exchanger having its water element adapted to be conected V in the water-cooling circuit of the prime mover and its oil element adapted to be connected to the oil circuit of the transmission; a cooling water radiator; a first twoway differential-acting valve for dividing the flow of cooling water from the prime mover water jacket between the inlets to said radiator and to said water element; a by-pass circuit between the outlet from the prime mover water jacket and the inlet to said radiator; a change-over valve controlling the inlets to said first two-way valve and said by-pass circuit; a second two-way differentialacting valve for dividing the flow of cooling water from said radiator to inlets to said water jacket and to said 'water element; a first temperature-sensitive element in the outlet from said water jacket for controlling the position of said first two-way valve, and a second temperature-sensitive element in the outlet from said oil element for controlling the position of said second two-way valve and the position of said'change-over' valve.

5. ,A heat exchange system for a working fluid having a poor rate of heat exchange with air directly, comprising a heat exchanger having working fluid and water elements each beingarranged to close progressively as the other opens progressively. The-system according to the present invention is applicable to cases where working liquids other than water 7 and oil are involved, and where one such'liquid is harder to cool in an air/liquid heat exchanger than the other.

We claim; y 1. For use in an hydraulic power transmission system adapted to be driven by ja water-cooled prime mover, a

in combination with a water circuit including a main water/air radiator having water inlet and outlet connections; a two-way differential-acting valve having its inlet connected'in circuit with the outlet from said water element, one outlet connected to the inlet to said water element, and the other outlet connected to the inlet to said radiator; a return flow connection from the outlet of said radiator shunting. said water element; water temperature sensitive means for controlling the position of said two-way valve, and "means for circulating water through said water circuit. 7

6. A heat exchange system as claimed in claim including an auxiliary water/air radiator; a second twoway differential-acting valve having its inlet connected to the outlet of said main radiator, one outlet connected to said return flow shunt circuit and the other outlet connected to the inlet to said auxiliary radiator, and

temperature sensitive means in the outlet from said working fluid heat exchange element for controlling the position of said second two-way valve.

7. In a hydraulic transmission system powered by a water-cooled prime mover, the combination with a conventional main cooling water, radiator of a heat exchanger having oil and water elements, the former connected in the oil circuit of the hydraulic transmission and the latter in the cooling water circuit; a first two-way differential-acting valve at the inlet to said radiator and connected so as to divide the flow of cooling water in varying proportions between said radiator and said water element; a thermostat in said cooling water circuit for governing the setting of said first two-way valve;

an auxiliary radiator in the cooling Water circuit having its outlet connected to the inlet of said water element; a second two-Way diflerential-acting valve connected to the outlet of said main radiator so as to divide the flow of cooling water therefrom in varying proportions between said auxiliary radiator and a point in said cooling water circuit beyond said water element, and a thermostat in the outlet from said oil element for governing the setting of said second two-way valve.

8. The combination as claimed inclaim 7 including a by-pass circuit around the first two-way valve for directing cooling water to the inlet to said main radiator; a change-over valve for selectively connecting either said bypass or said first two-way valve in the cooling water circult, and a connection between said oil element outlet thermostat and said change-over valve for controlling said selective connection.

9. An hydraulic power transmission system comprispump; a coolant jacket in said prime mover; a main coolant radiator; a coolant circuit interconnecting said jacket and said radiator; a fluid/ coolant heat exchanger having an hydraulic fluid element and a coolant element in heat exchange relation, said fluid element being connected in circuit with said fluid transmission circuit and said coolant element being connected in the return flow portion of said coolant circuit; a first two-way differential-acting valve having its inlet port connected to the outlet from said jacket, a first outlet port connected to the inlet to said main coolant radiator, and a second outlet port connected to the inlet to said coolant element; a connection between the outlet from said main coolant radiator and the inlet to said jacket; a thermostat in the outlet from said jacket for governing the setting of said first two-Way valve; an auxiliary coolant radiator having its outlet connected to the inlet to said coolant element; a second two-way differential-acting valve having its inlet port connected to the outlet from said main radiator, a first outlet port connected to the inlet to said jacket, and a second outlet port connected to the inlet to said auxiliary coolant radiator, and a thermostat in the outlet from said hydraulic fluid element for governing the setting of said second two-way valve.

10. An hydraulic power-transmission system as claimed in claim 9 including a by-pass for said first two-way valve for supplying coolant direct from said jacket to the inlet to said main coolant radiator; a change-over valve having its inlet port connected to the outlet from said jacket, a first outlet port connected to the inlet port of said first two-way valve and a second outlet port connected to said bypass, and a connection between said hydraulic fluid thermostat for governing the setting of said change-over valve.

References Cited by the Examiner V UNITED STATES PATENTS 2,696,074 12/54 Dolza -12 2,955,917 10/60 Roberts etal 60-50X JULIUS E. WEST, Primary Examiner.

EDGAR W. GEOGHEGAN, Examiner. 

1. FOR USE IN A HYDRAULIC POWER TRANSMISSION SYSTEM ADAPTED TO BE DRIVEN BY A WATER-COOLED PRIME MOVER, A HEAT EXCHANGE SYSTEM COMPRISING AN OIL/WATER HEAT EXCHANGER HAVING ITS WATER ELEMENT ADAPTED TO BE CONNECTED IN THE WATER COOLING CIRCUIT OF THE PRIME MOVER AND ITS OIL ELEMENT ADAPTED TO BE CONNECTED TO THE OIL CIRCUIT OF THE TRANSMISSION; A COOLING WATER RADIATOR; A TWO-WAY DIFFERENTIAL-ACTING VALVE FOR DIVIDING THE TOTAL FLOW OF COOLING WATER IN VARYING PROPORTIONS BETWEEN SAID RADIATOR AND SAID HEAT EXCHANGER WATER ELEMENT AND HAVING ITS INLET CONNECTED TO THE OUTLET OF THE PRIME MOVER WATER JACKET, ONE OUTLET CONNECTED TO SAID RADIATOR AND THE OTHER OUTLET CONNECTED TO THE INLET OF SAID WATER ELEMETN; CONNECTIONS FROM THE OUTLET OF SAID RADIATOR TO SAID WATER ELEMENT AND TO THE INLET OF SAID WATER JACKET; AND TEMPERATURE-RESPONSIVE ELEMENTS IN THE OUTLET OF SAID WATER JACKET AND IN THE OUTLET OF SAID OIL ELEMENT FOR CONTROLLING THE FLOW OF WATER THROUGH SAID WATER ELEMENT. 